my first experience was with a friend's Hern cannon back in 1974 purchased on a steel carriage from Dixie Gun Works,
here is the email I received back form Joel Brown,
Hi Allen,
Thanks for your interest in Hern Cannon Barrels. We have been making cannon barrels for over thirty years and would love the opportunity to make one for you.
1) All Hern Barrels have cast-in-place steel liners. Our full scale barrels, such as 1841 Six Pounder, 10-Pdr Parrott Rifle, 20-Pdr Parrott Rifle, 1857 Napoleon, and 3" Ordnance Rifle are made with 1/2" Wall DOM (Drawn over Mandrel) Tubing and have a press-fit and welded breech plug. DOM Liners have the most consistent bore diameter and are stronger than HFS Tubing.
2) Our barrels are cast in a horizontal flask. The front of the liner is held in a core-print in the mold, and the rear of the liner is centered in the mold by rows of welded spacers called chaplets. This prevents any shift in the liner during the casting process. The liner is shotblasted prior to attachment of the chaplets and fitting of the breech plug to remove any oxides and to promote bonding of the iron with the liner.
Please feel free to call me at 800-228-7794 if you have any other questions.
Best Regards,
Joel Brown